This invention relates to a multi-range gas flowmeter. Conventional multi-range flowmeters measure the gas flow by sensing parameters of the flow in the main flow path. U.S. Pat. No. 3,321,970 to Walker, and U.S. Pat. No. 3,037,384 to Good, which are directed to flowmeters which measure the flow rate by sensing a pressure differential across an orifice, disclose devices which place different sized orifices in the main flow path to accommodate different ranges of flow rate.
Other types of flowmeters, such as those which sense the change in temperature of the flowing gas caused by the addition of a fixed amount of heat, utilize a bypass or secondary flow path for the measurement of the flow rate. Because such a flowmeter, as described in U.S. Pat. No. 3,851,526 to Drexel, diverts only a relatively minor portion of the flow through the secondary path, the accuracy of the flowmeter degrades at very low flow rates.